Beetles in a suburban environment

There is nothing unusual about making an effort to get to know the neighbours when moving into a new area, unless you happen to have the interests and devotion of Dr Willy Kuschel, a research associ­ate with the Department of Scientific and Industrial Research in Auckland.

Dr Kuschel took up a position as an insect taxonomist at the Mount Albert Research Centre in late 1973, and moved into the Lynfield area of West Auckland. There it took him 15 years to familiarise himself with most of those around him whom he was keen to meet.

It is not that Willy Kuschel is an antisocial man; rather, he spent all that time seeking out not people, but beetles. To his surprise, and others’ astonishment, he has discovered nearly a thou­sand species in just the Lynfield district, and estimates that there are more than a hundred species still to be found.

The large numbers are perhaps not quite so surprising, for several recently published studies around the world have indicated that, with our knowledge of insects, and beetles in particular, we might only just be scratch­ing the surface.

It has been possible to make estimates of the likely numbers of species of some animal groups from the known species and current rates of discovery. Gener­ally, the latter decreases as our knowledge increases and techniques improve. Accordingly, taxonomists are not expecting to find many more species of birds or mammals, and only small numbers of reptiles.

However, although a massive three quarters of a million species of insects have already been de­scribed and named (out of a total list of 1.8 million identified animals) recent work has indicated that these are mostly species that have been found in places where it has been most convenient for scientists to look.

With the much publi­cised destruction of our world’s tropical rain forests in central and southern America, Africa and the Far East has come a heightened interest in these habitats, and the realisation that they have associated microfaunal communities that are virtually unknown. Recent estimates have put the likely number of insect species as high as 10 million, and some say that 50 million might be more realistic. Of these, beetles are the most common; in fact, there are more species of beetle than of any other creature on earth.

Painstaking investiga­tions like Dr Kuschel’s give some support to these extravagant claims. Of his final tally of 982 different beetle species (including 753 endemic and 229 foreign species) 22 species new to science have already been described from the Lynfield area, and another 130 indigenous species have yet to be described and named.

In the published account of his work, Dr Kuschel distinguishes 20 different beetle habitats and shows that many beetles are strictly limited in their distribution. In many instances, beetles which were found in native bush remnants were never recorded from adjacent gardens, even where suitable native trees had been planted.

As many endemic species, unlike most foreign immigrants, are flightless, they are evidently confined to the bush and are unable even to traverse corridors the width of a bulldozer blade, let alone reach the next isolated bush block. This fact highlights the importance of protecting even small parcels of bush as they are likely reservoirs of many native species which cannot relocate or survive elsewhere.

Nearly half of all beetle species are found on the foliage of trees and bushes and are captured by beating the vegetation gently so that the inhabitants fall off on to a sheet or tray placed below. Distinct species are found on the trunks of trees, especially those which have epiphytic growths of ferns, mosses, lichens and lianes or have deeply fissured bark.

Undergrowth plants, as well as open grassland and swamp plants, also have a good diversity, with many of the beetles being host-specific to particular plants such as liverworts, raupo, flax or sedges.

Only a few species attack live wood, but the opening up of freshly felled or recently dead wood by beetles and weevils is an important precursor to fungal and bacterial decay, allowing water and spores to enter the timber.

In well decayed wood, thoroughly impregnated by fungi and bacteria, there is always a rich fauna of insects, worms and mites. The feeding opportunities for fungus-eating and predatory beetles are plentiful, and representa­tives from nine different families utilise them. Among these is one of a number of newly discov­ered species, Microscydmus lynfieldi which, at no more than 0.6mm in length, is one of the smallest beetles in the world.

The so-called “wood-mould”, a granular soil-like medium that accumulates in trunk hollows, is a distinct habitat for a dozen species, while the larvae and adults of several dozen more feed directly on fungal tissues, often on the fruiting bodies of mush­rooms and toadstools and on bracket and jelly fungi, rusts and moulds.

Most interesting in this group are those that carry their own fungi as spores, to be cultured like edible wall-paper on the walls of the tunnels that they bore. These fungi are known as “ambrosia”, a reference to the ancient Greeks’ elixir of life, and thrive in the beetles’ tunnels, lining the walls with a carpet of fungal threads that the adults and larvae eat.

In leaf litter, which also contains the remnants of fallen flowers and fruits, as well as bird and insect droppings, there is a rich source of food for many beetles. Most are flightless, and many are new discov­eries. In contrast, beetles that live in garden compost, which might be thought to be a similar habitat, are mostly flying foreign species.

In open grasslands and gardens are beetles from many families: tiger beetles, scarabs, rove beetles, ladybirds, ant beetles, fungus weevils and leaf beetles. Some feed on grasses and other plants, and are well known for the damage they do to pastures, and some, like the familiar ladybirds and tiger beetles, are predators.

There are some beetles whose entire lives are spent underground. They are blind, wingless and quite unpigmented—true coleopteran troglodites that required the development of special underground pit traps to catch them.

The dung of sheep and fowls on pastoral and cultivated land forms other microhabitats with their own distinct beetle fauna. Other specialist beetles seek out carrion; one is appropriately named Necrophilus—death lover.

Waterways have their own characteristic beetle fauna, too. Along the stream beds, where there are both clean gravels and silted flood regions, several distinct species of rove and ground beetles are found. Bush streams provide breeding grounds for beetles with aquatic larvae, and ponds and cattle troughs are inhabited by true water beetles, which are fearsome predators both as larvae and adults.

Lynfield has a coastal aspect on to the lower reaches of the Manukau Harbour, and at the top of sandy beaches are to be found some of the first beetles discovered and identified in New Zealand, picked up by the scientists accompanying Captain Cook during his first voyage of exploration on the Endeavour in 1769. Lower down on the shel­tered Lynfield shores are other species that hide in air pockets in gravel when the tide is in, and scurry up and down at the water’s edge or live amongst the algal seaweed wrack when it is out.

Dr Kuschel’s study opens up a part of New Zealand’s natural heritage that has been long over­looked and shows it to be remarkably diverse in number, form and habit. If so many species have been found in such a small area, where they seem to have colonised almost every available niche, how many must there be throughout the whole of New Zealand?

Asked by a curious clergyman what he had learnt from his studies of the natural world, the eminent English biologist, J B S Haldane is said to have replied, “That God has an inordinate fondness of beetles”. Clearly, Willy Kuschel has too.